1. Field of the Invention
The present invention relates to power amplifiers, and more particularly, to a power amplifier that can maintain a constant gain by detecting a level of a signal being input and a level of a signal being output.
2. Description of the Related Art
Mobile communications terminals have been widely used due to their easy of use.
In order to transmit and receive RF signals, a mobile communications terminal uses a power amplifier. This power amplifier amplifies a signal while maintaining linearity, which is one of the main functions thereof.
Meanwhile, the characteristics of the power amplifier may be deteriorated since the power amplifier cannot perform an amplification operation in which the power amplifier amplifies a signal while maintaining linearity due to changes in operation regions caused by semiconductor processes, changes in temperature, and other environmental factors.
In order to prevent this deterioration in the characteristics of the power amplifier, an appropriate bias voltage needs to be applied to the power amplifier.
To this end, in the related art, ambient temperature is detected using a thermistor, and a bias voltage level is changed according to a change in temperature so that the changed bias voltage level is applied to the power amplifier. However, the detection of changes in temperature by using a thermistor may be inaccurate. Also, when the bias voltage level does not change linearly according to changes in temperature, the power amplifier still cannot perform an amplification operation while maintaining linearity. Furthermore, a method of detecting a level of a signal being output from a power amplifier and changing a bias voltage level to thereby increase efficiency merely increases efficiency but cannot change a bias voltage level according to changes in environment, thereby causing a deterioration in linearity.